The present invention relates to a display apparatus, and more specifically, to a plasma display panel (PDP) and digital micromirror device (DMD) display drive pulse controller.
A display apparatus of a PDP and a DMD makes use of a subfield method, which has binary memory, and which displays a dynamic image possessing half tones by temporally superimposing a plurality of binary images that have each been weighted. The following explanation deals with PDP, but applies equally to DMD as well.
A PDP subfield method is explained using FIGS. 1, 2, and 3.
Now, consider a PDP with pixels lined up 10 across and 4 vertically, as shown in FIG. 3. Let the respective R,G,B of each pixel be 8 bits, assume that the brightness thereof is rendered, and that a brightness rendering of 256 gradations (256 gray scales) is possible. The following explanation, unless otherwise stated, deals with a G signal, but the explanation applies equally to R, B as well.
The portion indicated by A in FIG. 3 has a signal level of brightness of 128. If this is displayed in binary, a (1000 0000) signal level is added to each pixel in the portion indicated by A. Similarly, the portion indicated by B has a brightness of 127, and a (0111 1111) signal level is added to each pixel. The portion indicated by C has a brightness of 126, and a (0111 1110) signal level is added to each pixel. The portion indicated by D has a brightness of 125, and a (0111 1101) signal level is added to each pixel. The portion indicated by E has a brightness of 0, and a (0000 0000) signal level is added to each pixel. Lining up an 8-bit signal for each pixel perpendicularly in the location of each pixel, and horizontally slicing it bit-by-bit produces a subfield. That is, in an image display method, which utilizes the so-called subfield method, by which 1 field is divided into a plurality of differently weighted binary images, and displayed by temporally superimposing these binary images, a subfield is 1 of the divided binary images.
Since each pixel is displayed using 8 bits, as shown in FIG. 2, 8 subfields can be achieved. Collect the least significant bit of the 8-bit signal of each pixel, line them up in a 10xc3x974 matrix, and let that be subfield SF1 (FIG. 2). Collect the second bit from the least significant bit, line them up similarly into a matrix, and let this be subfield SF2. Doing this creates subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8. Needless to say, subfield SF8 is formed by collecting and lining up the most significant bits.
FIG. 4 shows the standard form of a 1 field PDP driving signal. As shown in FIG. 4, there are 8 subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8 in the standard form of a PDP driving signal, and subfields SF1 through SF8 are processed in order, and all processing is performed within 1 field time.
The processing of each subfield is explained using FIG. 4. The processing of each subfield constitutes setup period P1, write period P2 and sustain period P3. At setup period P1, a single pulse is applied to a sustaining electrode, and a single pulse is also applied to each scanning electrode (There are only up to 4 scanning electrodes indicated in FIG. 4 because there are only 4 scanning lines shown in the example in FIG. 3, but in reality, there are a plurality of scanning electrodes, 480, for example.). In accordance with this, preliminary discharge is performed.
At write period P2, a horizontal-direction scanning electrodes scans sequentially, and a predetermined write is performed only to a pixel that received a pulse from a data electrode. For example, when processing-subfield SF1, a write is performed for a pixel represented by xe2x80x9c1xe2x80x9d in subfield SF1 depicted in FIG. 2, and a write is not performed for a pixel represented by xe2x80x9c0.xe2x80x9d
At sustain period P3, a sustaining pulse (driving pulse) is outputted in accordance with the weighting value of each subfield. For a written pixel represented by xe2x80x9c1,xe2x80x9d a plasma discharge is performed for each sustaining pulse, and the brightness of a predetermined pixel is achieved with one plasma discharge. In subfield SF1, since weighting is xe2x80x9c1,xe2x80x9d a brightness level of xe2x80x9c1xe2x80x9d is achieved. In subfield SF2, since weighting is xe2x80x9c2,xe2x80x9d a brightness level of xe2x80x9c2xe2x80x9d is achieved. That is, write period P2 is the time when a pixel which is to emit light is selected, and sustain period P3 is the time when light is emitted a number of times that accords with the weighting quantity.
As shown in FIG. 4, subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8 are weighted at 1, 2, 4, 8, 16, 32, 64, 128, respectively. Therefore, the brightness level of each pixel can be adjusted using 256 gradations, from 0 to 255.
In the B region of FIG. 3, light is emitted in subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, but light is not emitted in subfield SF8. Therefore, a brightness level of xe2x80x9c127xe2x80x9d(=1+2+4+8+16+32+64) is achieved.
And in the A region of FIG. 3, light is not emitted in subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, but light is emitted in subfield SF8. Therefore, a brightness level of xe2x80x9c128xe2x80x9d is achieved.
For a screen with overall bright luminance, it is possible to create a bright picture even using as-is a drive pulse acquired from a picture signal, but if an image becomes dark overall, when a drive pulse acquired from a picture signal is used as-is, it results in an extremely dark screen, and a weak picture rendition. The structure of the human eye is such that in bright places the pupil becomes smaller, reducing the amount of light that enters, but when it becomes dark, the pupil continuously enlarges so as to take in more light. To achieve the same effect thereas, there is a well-known method, by which, when a screen darkens overall, a drive pulse number is increased at the same ratio over the entire screen, making an entire screen bright, and rendering a robust picture while maintaining a dark atmosphere.
With regard to the brightness of an overall screen, there is a well-known method, which divides the transition from a bright situation to a dark situation into a plurality of stages, for example, 3 stages, bright, rather bright, dark, and for a bright situation utilizes a 1-times mode (FIG. 4), which uses a drive pulse as-is, for a rather bright situation, utilizes a 2-times mode (FIG. 6), which doubles a drive pulse, and for a dark situation, utilizes a 3-times mode (FIG. 7), which triples a drive pulse This is disclosed, for example, in the Japanese Patent specification of Kokai No. (1996)-286636 (corresponding to the specification of U.S. Pat. No. 5,757,343).
Thus, since a drive pulse is changed in stages, when a screen changes from a certain stage to another stage, for example, from rather bright to dark, an abrupt change is displayed on a screen, occasioning a sense of incongruousness.
A well-known approach is to adjust a fixed multiplication factor of gain with an object of doing away with the abrupt change of this screen, and performing continuous luminance adjustment (For example, the specification of Kokai No. (1996)-286636 (corresponding to the specification of U.S. Pat. No. 5,757,343)). The problem has been that even if a fixed multiplication factor of gain is changed, since a drive pulse is changed in stages to 2-times, 3-times, the sense of incongruousness of the screen at the point in time when the change occurs cannot be fully eliminated.
The present invention is designed to solve this problem, and has as a first object the provision of a PDP display pulse drive controller, which is capable of performing adjustments by changing a drive pulse using not only an integer multiplier, but also a multiplier of a value comprising a fraction, and of performing more continuous luminance adjustment.
An average level, peak level of brightness, PDP power consumption, panel temperature, contrast and such are used as parameters for rendering image brightness.
Performing adjustments by changing a drive pulse using not only an integer multiplier, but also a multiplier of a value comprising a fraction enables screen brightness adjustment that continuously brightens without intermittent brightness, so that a person watching a screen does not notice a change in brightness.
Further, the present invention has as a second object the provision of a PDP display drive pulse controller, which is capable of adjusting a subfield number in accordance with the brightness of an image (including both a dynamic image and a static image).
Increasing a subfield number makes it possible to do away with pseudo-contour lines, which are explained below. Conversely, decreasing a subfield number, while running the risk of generating pseudo-contour lines, makes it possible to create a clearer image.
Pseudo-contour noise is explained below.
Assume that regions A, B, C, D from the state shown in FIG. 3 have been moved 1 pixel width to the right as shown in FIG. 5. Thereupon, the viewpoint of the eye of a person looking at the screen also moves to the right so as to follow regions A, B, C, D. Thereupon, 3 vertical pixels in region B (the B1 portion of FIG. 3) will replace 3 vertical pixels in region A (A1 portion of FIG. 5) after I field. Then, at the point in time when the displayed image changes from FIG. 3 to FIG. 5, the eye of a human being is cognizant of region B1, which takes the form of a logical product (AND) of B1 region data (01111111) and A1 region data (10000000), that is (00000000). That is, the B1 region is not displayed at the original 127 level of brightness, but rather, is displayed at a brightness level of 0. Thereupon, an apparent dark borderline appears in region B1. If an apparent change from xe2x80x9c1xe2x80x9d to xe2x80x9c0xe2x80x9d is applied to an upper bit like this, an apparent dark borderline appears.
Conversely, when an image changes from FIG. 5 to FIG. 3, at the point in time when it changes to FIG. 3, a viewer is cognizant of region A1, which takes the form of a logical sum (OR) of A1 region data (10000000) and B1 region data (01111111), that is (11111111). That is, the most significant bit is forcibly changed from xe2x80x9c0xe2x80x9d to xe2x80x9c1,xe2x80x9d and in accordance with this, the A1 region is not displayed at the original 128 level of brightness, but rather, is displayed at a roughly 2-fold brightness level of 255. Thereupon, an apparent bright borderline appears in region A1. If an apparent change from xe2x80x9c0xe2x80x9d to xe2x80x9c1xe2x80x9d is applied to an upper bit like this, an apparent bright borderline appears.
In the case of a dynamic image only, a borderline such as this that appears on a screen is called pseudo-contour noise (xe2x80x9cpseudo-contour noise seen in a pulse width modulated motion picture displayxe2x80x9d: Television Society Technical Report, Vol. 19, No. 2, IDY95-21 pp. 61-66), causing degradation of image quality.
According to the present invention, a display apparatus creates, for each picture, Z subfields from a first to a Zth in accordance with Z bit representation of each pixel, a weighting value for weighting to each subfield, a multiplication factor A for amplifying a picture signal, and a number of gradation display points K, said display apparatus, comprising:
brightness detecting means for obtaining image brightness data; and
adjusting means for adjusting a weighting multiplier N, by which said weighting value is multiplied, on the basis of the brightness data, said weighting multiplier N comprising a positive integer, and a decimal fraction numerical value.
According to a preferred embodiment, said brightness detecting means comprises average level detecting means, which detect an average level (Lav) of image brightness.
According to a preferred embodiment, said brightness detecting means comprises peak level detecting means, which detect a peak level (Lpk) of image brightness.
According to a preferred embodiment, said adjusting means comprises image characteristic determining means, which decide a fixed multiplication factor A, which brightens or darkens the brightness of an entire image by amplifying a picture signal, and multiplication means (12), which amplify a picture signal A times based on fixed multiplication factor A.
According to a preferred embodiment, said adjusting means comprises image characteristic determining means, which decide total number of gradations K, and display gradation adjusting means, which change a picture signal to the nearest gradation level based on total number of gradations K.
According to a preferred embodiment, said adjusting means comprises image characteristic determining means, which decide a subfield number Z, and corresponding means, which decide a weighting of each subfield on the basis of the subfield number Z.
According to a preferred embodiment, the weighting multiplier N is increased as said average brightness level (Lav) decreases.
According to a preferred embodiment, the subfield number Z is reduced as said average brightness level (Lav) decreases.
According to a preferred embodiment, the fixed multiplication factor A is increased as said average brightness level (Lav) decreases.
According to a preferred embodiment, the multiplication result of the fixed multiplication factor A and weighting multiplier N is increased as said average brightness level (Lav) decreases.
According to a preferred embodiment, the weighting multiplier N is reduced as said peak brightness level (Lpk) decreases.
According to a preferred embodiment, the subfield number Z is increased as said peak brightness level (Lpk) decreases.
According to a preferred embodiment, the fixed multiplication factor A is increased as said peak brightness level (Lpk) decreases.
According to a preferred embodiment, said brightness detecting means comprises contrast detecting means, which detect image contrast.
According to a preferred embodiment, said brightness detecting means comprises ambient illumination detecting means, which detect ambient illumination, where a display apparatus is located.
According to a preferred embodiment, said brightness detecting means comprises power consumption detecting means, which detect display panel power consumption of a display apparatus.
According to a preferred embodiment, said brightness detecting means comprises temperature detecting means, which detect display panel temperature of a display apparatus.
According to a preferred embodiment, the weighting value of each subfield Q is multiplied by a weighting multiplier N of each subfield, and an integer value obtained by rounding off to a decimal place the product thereof is used as a number of light emissions of each subfield.
According to a preferred embodiment, the apparatus further comprises means for generating for each gradation correction data that accords with an error between a luminance of an image to be displayed, and displayable luminance in accordance with the number of light emissions of each subfield, and means for changing a spatial density of a gradation, which is displayed in accordance with this correction data.
According to a preferred embodiment, said correction data generating means is constituted from a correction data conversion table, a correction data of which is correspondent to each gradation.
According to a preferred embodiment, said means for changing spatial density actuates only a low luminance portion.
According to a preferred embodiment, said means for changing spatial density comprise a dither circuit.
According to a preferred embodiment, said means for changing spatial density is an error diffusing circuit.